某些含硫/氮杂原子的有机半导体材料分子设计及载流子传输性质理论研究

【作者】 赵蔡斌；

【导师】 王文亮；

【作者基本信息】 陕西师范大学 ， 物理化学， 2014， 博士

【摘要】 近几十年以来,有机光电材料因其质轻、价廉、性质可调、能大面积制备等优势在微电子器件中得到了广泛的应用。大量理论和实验研究表明,电荷载流子传输效率是影响有机半导体器件性能至关重要的因素,因此从理论上研究有机半导体材料载流子迁移率对设计和开发具有特殊功能的新型有机光电材料具有重要的理论与实践意义。本论文以几类含硫、氮杂原子的有机小分子光电材料分子设计及载流子迁移率理论模拟为主要研究内容,在分子和晶体水平上深入分析了所研究化合物分子结构(如取代基)、电子性质(如前线分子轨道能级、电离势和电子亲和势)、固态分子堆积模式(如晶体结构)等因素对其电荷传输性质的影响。另外,我们也讨论了取代基对光谱性质的影响。本文研究为设计和合成具有高载流子迁移率和空气稳定性的有机光电材料提供了理论参考。论文主要包括以下四部分内容：1.以蒽并[2,3-c]噻吩(AcTH)为基本结构单元,设计并研究了一系列5,10--取代的蒽并[2,3-c]噻吩衍生物分子结构、电子性质、光学稳定性、内重组能和载流子迁移率等性质。计算结果表明,氰基取代和乙炔化能增强母体化合物分子刚性,是设计低重组能有机半导体材料的有效方法。此外,还利用简单的一维电荷传输模型和半经验的Marcus-Hush电子转移速率理论,在分子水平上评估了化合物AcTH、DCHC-AcTH、DCN-AcTH的空穴迁移率,并与相同条件下Pentacene的预测值进行了比较。结果表明,这三个化合物在同一评估模型中表现出比Pentacene更强的空穴传输能力。尽管模型本身较为简单,但结果预示AcTH、DCHC-AcTH. DCN-AcTH应该是性能良好的空穴传输材料,值得进一步实验研究。2.研究了7,8,15,16-tetraazaterrylene(TAT)及其系列吸电子基(-Cl,-F,-CN)四取代衍生物分子结构、电子性质、光谱性质和电子迁移率等信息。研究发现氟基(-F)、氯基(-C1)、氰基(-CN)等强吸电子基的引入能显著降低化合物前线分子轨道能级和电子注入势垒,提高其氧化-还原稳定性,并且引入这些基团也能增强主电荷传输通道的电子转移积分,从而提高这类材料的电子传输能力。特别是4CN-TAT绝热电子亲和势高达3.599eV,预计是相当稳定的电子传输材料。采用量子校正的Marcus-Levich-Jortner(MLJ)电子转移速率模型结合随机行走模拟和Einstein方程预测了TAT晶体的载流子迁移率。结果表明,TAT单晶室温下(300K)电子迁移率达到3.404×10-2cm2·V-1·s-1。吸收和发射光谱模拟表明,引入吸电子取代基致使最大吸收和发射峰红移,光吸收和发射强度增大,其中最强吸收和发射峰均归属于HOMO和LUMO轨道之间的电子跃迁。3.以2-((10H-benzothieno[3,2-b]indol-2-yl)methylene)malononitrile(BTMN)和2-((11H-benzo[a]carbazol-9-yl)methylene)malononitrile(BCMN)为研究对象,采用量子校正的Marcus-Levich-Jortner(MLJ)电子传输速率模型和Einstein方程,研究了分子晶体BTMN和BCMN的空穴和电子迁移率。结果表明,BTMN晶体空穴迁移率室温下(300K)达到6.387×10-2cm-2·V-1·s-1,电子迁移率达到1.936×10-2cm2·V-1·-1;BCMN晶体空穴迁移率室温下达到2.404×10-1cm2·V-1·s-1,电子迁移率达到1.418×10-1cm2·V-1·s-1.预测结果表明两种分子晶体空穴和电子迁移率均比较大,而且处在同一数量级上。尤其是BCMN,两种载流子迁移率预测值均超过具有实际应用价值的OFET装置载流子迁移率临界值(0.1cm2·V-1·s-1),因此BCMN是非常有应用前景的两极传输材料,值得实验上进一步器件化研究。吸收和发射光谱模拟表明,最强吸收和发射峰均归属于HOMO-1和LUMO轨道之间的电子跃迁,光吸收／发射过程为光诱导的分子内电子在并四环和二氰乙烯基之间的转移过程。4.利用密度泛函理论(DFT)计算结合晶体结构预测和不连续的电荷跳跃模型,在分子和晶体水平上研究了四个氮掺杂二氰基取代的并五苯洐生物(PBD1, PBD2, PBD3, PBD4)分子结构、电子性质、晶体结构及电子传输参数。结果表明,氮原子掺杂及氰基取代不但不会破坏并环体系骨架结构,而且能显著降低体系的HOMO和LUMO分子轨道能级,是设计高空气稳定电子传输材料的合理策略。晶体结构预测表明,所研究化合物在晶体中可沿某些晶轴方向形成近距离的面对面分子堆积。以预测的分子晶体结构为基础,采用传统的Marcus-Hush电荷传输模型和Einstein方程研究了其电子迁移率。结果表明,所研究晶体室温下(300K)具有较高的电子迁移率(0.518～1.052cm2·V-1·s-1),是一类相当有应用前景的电子传输材料,值得实验上进一步合成并器件化研究。迁移率各向异性模拟表明,电子在这些分子晶体中传输时表现出显著的各向异性行为,电子迁移率最大值沿着晶轴方向。更多还原

【Abstract】 In the last decades, organic photoelectron materials have been widely used in microelectronic devices for several obvious advantages, such as lightweight, low-cost, flexible adjustion of properties, and convenient large-area fabrication. Numerous theoretical and experimental investigations have demonstrated clearly that the charge carrier transport effeciency is the most important factor that determines the performance of photoelectron devices. Hence, it is very significant to theoretically investigate the charge carrier mobility of organic photoelectron materials for designing and developing new organic semiconductor materials with some special functions. In this dissertation, based upon the systematical study on the the molecular design and charge carrier mobility for several newly-synthesized small molecules containing sulfur and nitrogen heteroatoms, we have analyzed in detail the influences of molecular geometries (such as substituents), electronic properties (such as frontier molecular orbital levels, ionization potentials, and electron affinities), and molecular packing patterns in solid phases (such as crystal structures) on the charge carrier mobility at the molecular and crystal levels. In addition, the substituent effects on the light absorption and emission properties of these compounds have also been discussed. Our study may provide several valuable references for designing and synthesizing new photoelectronic materials with the high carrier mobility and air stability. The whole dissertation mainly includes the following four sections,1. Based on anthra[2,3-c]thiophene unit (AcTH), a set of5,10-disubstituted anthra [2,3-c]thiophene derivatives have been designed, and their molecular structures, electronic properties, optical stability, inner reorganization energies, and hole mobilities have been investigated. Our calculations reveal that cyano group substitution and ethinylation, which can enhance the molecular rigidity of parent compound, are efficient strategies designing organic semiconductor materials with the low inner reorganization energy. In addition, upon the simple one dimensional charge transport model and semiempirical Marcus-Hush electron transfer theory, the hole mobilities of AcTH, DCHC-AcTH, and DCN-AcTH have been estimated and compared with that of Pentacene. The result shows that these three compounds have higher hole mobilities under the same condition than Pentacene, which indicates AcTH, DCHC-AcTH, and DCN-AcTH may be promising p-channel OFET materials and worthy of being studied further in experiments.2. The molecular geometries, electronic properties, spectral properties, and electron mobilities have been studied for7,8,15,16-tetraazaterrylene (TAT) and its three tetrasubstituted derivates with the electron-withdrawing groups (-F,-Cl,-CN). Our calculation shows that the introduction of strong electron-withdrawing groups can remarkably lower the frontier molecular orbital energy levels and the electron injection potential barrier, and enhance the oxido-reduction stability. More important, introducing these groups can also increase the hole and electron transfer integrals in the dominant charge transfer channel, and then the electron transport ability. Especially,4CN-TAT possesses a quite large adiabatic electron affinity of3.599eV, and so it is very stability as n-channel OFET materials exposed to water and oxygen. Lastly, upon the quantum-corrected Marcus-Levich-Jortner (MLJ) rate model coupled with the random-walk simulation of diffusion coefficient and the Einstein equation, the electron mobility for TAT molecular crystal is predicted to be as high as3.404×10-2cm2·V-1·s-1, which suggestes that TAT crystal may be a promising n-channel OFET material and is worthy of being studied further in experiments. In addition, the simulation for the spectral properties indicates that the strongest absorption and emission peaks red shift with the introduction of electron-withdrawing groups and these peaks are dominated by the transition between HOMO and LUMO.3. Based on two newly-synthesized small molecular compounds with the dicyanovinyl group, including BTMN and BCMN, the hole and electron mobilities have been theoretically investigated with the quantum-corrected Marcus-Levich-Jortner (MLJ) electron transfer rate formulation and the Einstein equation. The results show that the hole and electron mobilities at room temperature (T=300K) reach6.387×10-2cm2·V and1.936×10-2cm2·V-1·-s-1for BTMN crystal,2.404×10-1cm·V-1·-s-1and1.418×10-1’cm2·V-1·s-1for BCMN crystal. Our prediction reveals that BTMN and BCMN should be potential ambipolar transport OFET materials for their close hole and electron mobilities. More important, BCMN crystal displays large carrier mobilities, which are even more than the threshold value of0.1cm2·V-1·s-1, that is enough high for applying in practical OFET devices. Hence, BCMN is expected to be promising ambiploar transport materials and deeply be studied in experiments. In addition, the simulation for the light absorption and emission properties indicates that the strongest absorption and emission peaks are mainly dominated by the transition between HOMO-1and LUMO. Practically, the light absorption and emission in the studied compounds are the intramolecular electron transfer process induced by light between the fused ring and the dicyanovinyl group.4. In this section, the molecular structures, electronic properties, crystal structures, and electron transport parameters for four novel nitrogen-rich pentacene derivatives with two cyano groups (PBD1, PBD2, PBD3, and PBD4) have been investigated at the molecular and crystal levels by means of density functional theory (DFT) calculations coupled with the prediction of crystal structures and the incoherent charge-hopping model. Calculations reveal that the nitrogen doping and cyano group substitution can lower remarkably the HOMO and LUMO energy levels, and do not break the parent’s planar structure, then which are viewed as the efficient strategies designing organic electron transport materials with the high air-stability. The prediction of crystal.--structures indicates that these compounds in crystals can stack the close face-to-face style with the short interplanar distance along the crystal axis direction. In addition, based on the crystal structures obtained with the molecular mechanics (MM) method coupled with the Marcus-Hush charge transfer model and the Einstein equation, the electron mobility of these molecular crystals have been studied. Our calculations show that these crystals may be potential n-channl OFET materials for their high electron mobility (0.518～1.052cm2·V-1·s-1), and worthy of being investigated further in experiments. Furthermore, we find the electron transport in these crystals shows remarkable anisotropic, and the maximum μe value appears along a certain crystal axis direction.更多还原